Probing the nonstrange quark star equation of state with compact stars and gravitational waves

TL;DR

This paper revises the perturbative QCD model to resolve thermodynamic inconsistencies and explores the implications for the maximum mass of up-down quark stars, with relevance to observed compact objects and gravitational wave events.

Contribution

It introduces a new term in the thermodynamic potential density to fix inconsistencies and applies this to constrain quark star properties based on astrophysical observations.

Findings

Maximum mass of $ud$ quark star can reach 2.17 $M_{\u03A9}$ without tidal constraints.

Observed 2.14 $M_{\u03A9}$ pulsar could be an $ud$ quark star.

GW190814's compact object cannot be an $ud$ quark star under the revised model.

Abstract

A recent study shows that incorporating a new term into the thermodynamic potential density, as required by the thermodynamic consistency criterion, can effectively resolve the thermodynamic inconsistency problems of the conventional perturbative QCD model. This additional term plays a crucial role in resolving inconsistencies at relatively low densities and becomes negligible at extremely high densities. Within this revised perturbative QCD model, we find that if we require only that the energy per baryon of up-down ($ud$) quark matter exceeds 930 MeV so as not to contradict the standard nuclear physics, the maximum mass of an $ud$ quark star allowed by the revised perturbative QCD model can reach up to 2.17 $M_{\odot}$. From this perspective, the observed 2.14 $M_{\odot}$ pulsar PSR J0740+6620 may be an $ud$ quark star. However, if we further impose the constraint that the tidal deformability of a 1.4 $M_{\odot}$ $ud$ quark star must be consistent with the GW170817 event, the maximum mass allowed by the revised perturbative QCD model would decrease to no more than 2.08 $M_{\odot}$. Consequently, our results suggest that the compact object with a mass of 2.50-2.67 $M_{\odot}$, as observed in the GW190814 event, cannot be an $ud$ quark star, according to the revised perturbative QCD model.